This invention relates generally to thin film technology and more particularly to a method of producing high quality vanadium dioxide (V0.sub.2) thin films through a one-step reactive evaporation process.
It is generally known that V0.sub.2 is one of several transition metal oxides which show an abrupt change in certain physical properties such as electrical resistance at a temperature T.sub.t (transition temperature). In V0.sub.2, the transition is probably best described as a first-order semiconductor-to-metal transition accompanied by a lattice distortion with T.sub.t =68.degree. C. Because of this conveniently low transition temperature and the large drop in near infrared transmittance experienced by such films, V0.sub.2 has been used in thermal relays, electrical switching elements, and optical storage media.
Prior to 1970, V0.sub.2 thin films were usually produced by a variety of methods including pyrolysis, DC reactive sputtering, and a two-step physical evaporation of vanadium in an oxygen ambient followed by oxygen annealing. Since 1970, however, RF reactive sputtering has been used almost exclusively. While these processes produce a good quality film (i.e., a resistivity ratio of at least 5000), they nevertheless require complex monitoring of a large number of independent deposition variables and are relatively inflexible in their application with other simultaneous processes.